Currently, various techniques are employed for non-contact three-dimensional measurement of items that may part of either fabrication, or any other operation upon, any manner of work piece, of which dental surfaces provide one kind of example. Techniques of this sort may use optical beams projected onto the measured object along one or more paths. An example of an apparatus and method for performing such remote metrology is provided in U.S. Pat. No. 7,375,827 (to Sanilevici et al.), and that patent is incorporated herein by reference, however that patent is provided solely by way of example, and the teachings of this invention may advantageously be applied in many other contexts. Various coordinate measuring machines (CMMs) are known in the art, and they may provide measurements of the sort to which the present teachings may advantageously be applied. More particularly, the technique of conoscopic holography allows measurement of a distance from a fiducial point in space (otherwise referred to as a “fiducial reference”) to a point on the surface of an object, whereby the measurement is made along a single line of sight, which is scanned, in turn, across the object to obtain complete shape information. A mode of measurement along a line-of-sight coincident with an illuminating beam may be referred to, herein, as “coaxial.” Conoscopic holography may be performed using the ConoProbe™ sensor supplied by Optimet, Optical Metrology Ltd. of Jerusalem, Israel, however, again, particular measurement apparatus and techniques are cited merely by way of example.
In the industrial field, for example, articulated measurement arms may be employed, where an optical or mechanical measurement sensors are mounted on several articulated arms that are manipulated to measure the dimensions of a physical object. During or after measurement with such a system, measurement information is processed, analyzed and presented. For example, certain critical dimensions and values may be compared against computerized drawings, and a deviation map may be presented on a PC or similar screen. Such a system is shown in FIGS. 1A and 1B.
When 3-D measurements are performed optically, the results of the measurement are typically presented on a video monitor such as a PC screen (shown in FIG. 1B), or else the results are used to govern other processes or machinery. Derivative information may also be extracted from the 3-D measurements, including such information as dimensions, distances, angles, edges, positions, deviation from a given data set, etc. Such derivative information may be presented in the form of numbers or colors. One example includes a comparison of 3-D information derived from measurement to computer-aided-design (CAD) specifications, which may be resident in computer memory or computer-readable media.
Measurement systems of the foregoing type may also be used in the context of dental restoration, where various objects bearing on restoration may be scanned in order to provide accurate 3-D information for purposes of designing and manufacturing dental restorations with computerized manufacturing machines. In the dental application of CAD/CAM processing, for example, 3-D measurements may be made of teeth in the mouth, or, alternatively, 3-D measurements may be taken of dental casts by means of a desktop scanner. One such scanner, described in detail in U.S. Pat. No. 7,375,827, is shown in FIG. 1C. In that figure, numeral 62 designates a multi-position actuator which allows bending of a laser beam into different directions, with coaxial measurements performed along each direction. A scanned work piece 60 is moved by actuators 70 relative to the illuminating beam. Intra-oral 3-D scanning of teeth and gums provides another example of 3-D metrology, and, as taught in U.S. patent application Ser. No. 12/401,668, filed Mar. 11, 2009, may be based on conoscopic holography that provides successive distance measurements coaxial with an illuminating beam.
Following measurement, either intra-orally or by means of a desktop scanner, measurement data are then typically presented on a screen and certain design steps are taken, such as marking of a crown end line, or preparation line. Marking of the preparation line may be performed in real time on a computer screen. Additional steps include design of the entire shape of the restoration, determining the insertion axis of the crown to the mouth etc. That design information then provides the basis for the fabrication of dental restorations.
One of the problems of any of the foregoing prior art 3-D metrological methods is the problem of verifying whether the measurement and the design, based on the measurement information and the user's skills, are correct in relation to the real physical object of measurement since the results are not overlaid on the real physical object. A related problem is the difficulty of reviewing, in real time, the affect that changes or modifications in the design may have during the modifications process. For example, defining the preparation line of a dental crown or bridge is based not only on measurement information but also on software algorithms and user skills. Another problem left unaddressed by methods of the prior art is to the problem of detecting where exactly on a physical object itself, does it deviate from the article as designed or from a specified dimension.
Another problematic aspect of prior art equipment and practice is that the practitioner must be attentive to the object of measurement, which may be in one field of view of the practitioner, and, at the same time, must be attentive to the monitor where the results of the measurement are being displayed, in another field of view of the practitioner. The practitioner is required to divert his attention from one place to another and without correlation between the two (and thus may also lose track of a particular position).